An electrocardiogram (ECG) records electrical potentials in the heart using a standardized set format 12-lead configuration to record cardiac electrical signals from well-established chest locations. Electrodes are placed on the skin over the anterior thoracic region of the body to the lower right and to the lower left of the sternum, on the left anterior chest, and on the limbs. The recorded cardiac electrical activity, represented by PQRSTU waveforms, can be interpreted to derive heart rate and physiology, where each P-wave represents atrial electrical activity and the QRSTU components represent ventricular electrical activity.
An ECG is a snapshot of heart function, typically recorded over 12 seconds, that can help diagnose rate and regularity of heartbeats, effect of drugs or implantable cardiac devices, and whether a patient has heart disease. ECGs are limited to recording those heart-related aspects present at the time of recording. Thus, an ECG only provides a partial picture and can be insufficient for complete patient diagnosis of many cardiac disorders. Sporadic conditions that may not show up during a spot ECG recording, including fainting or syncope; rhythm disorders, such as tachyarrhythmias and bradyarrhythmias; asystolic episodes; and other cardiac and related disorders, require other means of diagnosis.
Diagnostic efficacy of cardiac rhythm disorders in particular can be improved, when appropriate, through long-term extended ECG monitoring. Recording cardiac physiology over an extended period can be challenging, yet is often essential to enabling a physician to identify events of potential concern. Although a 30-day observation period is considered the “gold standard” of ECG monitoring, achieving 30-day coverage has proven unworkable because conventional ambulatory ECG monitoring systems are arduous to employ, cumbersome to wear, and excessively costly. Nevertheless, if a patient's ECG could be recorded in an ambulatory setting over long periods of time, thereby allowing the patient to engage in activities of daily living, the chances of acquiring meaningful information and capturing an abnormal cardiac rhythm event becomes more likely to be achieved.
For instance, the long-term wear of ECG electrodes is complicated by skin irritation and the inability of conventional ECG electrodes to maintain continual skin contact after a day or two. Moreover, time, dirt, moisture, and other environmental contaminants, as well as perspiration, skin oil, and dead skin cells from the patient's body, can get between an ECG electrode, the non-conductive adhesive used to adhere the ECG electrode, and the skin's surface. These factors adversely affect electrode adhesion and the quality of cardiac signal recordings. Moreover, physical movement and clothing impart compressional, tensile, and torsional forces on electrode contact points decreasing signal quality, especially over long recording times. In addition, an inflexibly fastened ECG electrode is prone to dislodgement that often occurs unbeknownst to the patient, making the ECG recordings worthless. Further, some patients may have skin conditions, such as itching and irritation, aggravated by the wearing of most ECG electrodes. A patient may have to periodically remove or replace electrodes during a long-term monitoring period, whether to replace a dislodged electrode, reestablish better adhesion, alleviate itching or irritation, allow for cleansing of the skin, allow for showering and exercise, or for other purpose. Such replacement or slight alteration in electrode location can interfere with the goal of recording the ECG signal for long periods of time. Finally, such recording devices are often ineffective at recording atrial electrical activity, which is critical in the accurate diagnosis of heart rhythm disorders, because of the use of traditional ECG recording electronics or due to the location of the monitoring electrodes far from the origin of the atrial signal, for instance, the P-wave.
Conventionally, Holter monitors are widely used for long-term extended ECG monitoring, typically, for only 24-48 hours. A typical Holter monitor is a wearable and portable version of an ECG that includes cables for each electrode placed on the skin and a separate battery-powered ECG recorder. Similar to standard in-clinic ECG practice, the cable and electrode combination (or leads) are placed in the anterior thoracic region. The duration of a Holter monitoring recording depends on the sensing and storage capabilities of the monitor, as well as battery life. A “looping” Holter (or event) monitor can operate for a longer period of time by overwriting older ECG tracings, thence “recycling” storage in favor of extended operation, yet at the risk of losing crucial event data. Holter monitors remain cumbersome, expensive and typically for prescriptive use only, which limits their usability. Further, the skill required to properly place the ECG leads on the patient's chest hinders or precludes a patient from replacing or removing the electrodes.
The ZIO XT Patch and ZIO Event Card devices, manufactured by iRhythm Tech., Inc., San Francisco, Calif., are wearable stick-on monitoring devices that are typically worn on the upper left pectoral region to respectively provide continuous and looping ECG recordings. The location is used to simulate surgically implanted monitors. These devices are prescription-only for single patient use. The ZIO XT Patch device is limited to 14-day monitoring, while the ZIO Event Card device's electrodes can be worn for up to 30 days. The ZIO XT Patch device combines electronic recordation components, including battery, and physical electrodes into a unitary assembly that adheres to the skin. The ZIO XT Patch device uses adhesive strong enough to support the weight of both the monitor and the electrodes over an extended period of time. During monitoring, the battery is continually depleted and can potentially limit overall monitoring duration. The ZIO Event Card device is a form of downsized Holter monitor with a recorder component that must be removed during activities that could damage the non-waterproof electronics. These patches have a further limitation because of a small inter-electrode distance coupled to its designed location of application, high on the left chest. The electrical design of the ZIO patch and its location make recording high quality atrial signals (P-waves) difficult, as the location is relatively far from the origin of these low amplitude signals. As well, the location is suboptimal for identification of these signals. Furthermore, this patch is problematical for woman by being placed in a location that may limit signal quality, especially in woman with large breasts or bosoms. Both ZIO devices represent compromises between length of wear and quality of ECG monitoring, especially with respect to ease of long term use, female-friendly fit, and quality of atrial (P-wave) signals.
Personal ambulatory monitoring, both with smartphones or via adjuncts to smartphones, such as with a wirelessly-connected monitor or activity tracker, of varying degrees of sophistication and interoperability, have become increasingly available. For instance, McManus et al., “A Novel Application for the Detection of an Irregular Pulse using an iPhone 4S in Patients with Atrial Fibrillation,” Vol. 10(3), pp. 315-319 (March 2013), the disclosure of which is incorporated by reference, discloses obtaining pulsatile time series recordings before and after cardioversion using the digital camera built into a smartphone. An algorithm implemented as an app executed by the smartphone analyzed recorded signals to accurately distinguish pulse recordings during atrial fibrillation from sinus rhythm, although such a smartphone-based approach provides non-continuous observation and would be impracticable for long term physiological monitoring. Further, the smartphone-implemented app does not provide continuous recordings, including the provision of pre-event and post-event context, critical for an accurate medical diagnosis that might trigger a meaningful and serious medical intervention. In addition, a physician would be loath to undertake a surgical or serious drug intervention without confirmatory evidence that the wearer in question was indeed the subject of the presumed rhythm abnormality. Validation of authenticity of the rhythm disorder for a specified patient takes on critical legal and medical importance.
The AliveCor heart monitor, manufactured by AliveCor, Inc., San Francisco, Calif., provides a non-continuous, patient-triggered event monitor, which is worn on the fingertip. Heart rate is sensed over a single lead (comparable to Lead I on a conventional ECG) and recorded by an app running on a smartphone, such as an iOS operating system-based smartphone, such as the iPhone, manufactured by Apple Inc., Cupertino, Calif., or an Android operating system-based smartphone, manufactured and offered by various companies, including Google Inc., Mountain View, Calif.; Samsung Electronics Co., Ltd., Suwon, S. Korea; Motorola Mobility LLC, a subsidiary of Google Inc., Libertyville, Ill.; and LG Electronics Inc., Seoul, S. Korea. The Android operating system is also licensed by Google Inc. The app can send the data recorded by an AliveCor heart monitor from the smartphone to healthcare providers, who ultimately decide whether to use the data for screening or diagnostic purposes. Furthermore, as explained supra with respect to the McManus reference, none of these devices provides the context of the arrhythmia, as well as the medico-legal confirmation that would otherwise allow for a genuine medical intervention.
Similarly, adherents to the so-called “Quantified Self” movement combine wearable sensors and wearable computing to self-track activities of their daily lives. The Fitbit Tracker, manufactured by Fitbit Inc., San Francisco, Calif.; the Jawbone UP, manufactured by Jawbone, San Francisco, Calif.; the Polar Loop, manufactured by Polar Electro, Kempele, Finland; and the Nike+ FuelBand, manufactured by Nike Inc., Beaverton, Oreg., for instance, provide activity trackers worn on the wrist or body with integrated fitness tracking features, such as a heart rate monitor and pedometer to temporally track the number of steps taken each day with an estimation calories burned. The activity tracker can interface with a smartphone or computer to allow a wearer to monitor their progress towards a fitness goal. These activity trackers are accessories to smartphones, including iOS operating system-based smartphones, Android operating system-based smartphones, and Windows Phone operating-system based smartphones, such as manufactured by Microsoft Corporation, Redmond, Wash., to which recorded data must be offloaded for storage and viewing.
The features of activity trackers can also be increasingly found in so-called “smart” watches that combine many of the features of activity trackers with smartphones. Entire product lines are beginning to be offered to provide a range of fitness- and health-tracking solutions. As one example, Samsung Electronics Co., Ltd., offers a line of mobile products with fitness-oriented features, including the Galaxy S5 smartphone, which incorporates a biometric fingerprint reader and heart rate monitor; the Gear 2 smart watch, which also incorporates a heart rate monitor; and the Gear Fit wearable device, which incorporates a heart rate monitor, real time fitness coaching, and activity tracker. The Galaxy S5 smartphone's heart rate monitor is not meant for continuous tracking, while the both the Gear 2 smart watch and Gear Fit wearable device must be paired with a smartphone or computer to offload and view the recorded data.
With all manner of conventional “fitness-oriented” device, whether smartphone, smart watch, or activity tracker, quantified physiology is typically tracked for only the personal use of the wearer. Monitoring can be either continuous or non-continuous. The wearer must take extra steps to route recorded data to a health care provider; thus, with rare exception, the data is not time-correlated to physician-supervised monitoring nor validated. Furthermore, the monitoring is strictly informational and medically-significant events, such as serious cardiac rhythm disorders, including tachyarrhythmias and bradyarrhythmias, while potentially detectable, are neither identified nor acted upon.
In today's medical and legal environment, a mobile device, such as a smartphone, provides information that cannot be translated into data that triggers surgery or drug therapy by a physician. In the case of a smartphone detecting a fast heartbeat, for example, such a detection and the information on the smartphone would neither be identified as truly related to the patient in question or would be deemed sufficient for subjecting a patient to surgery or potentially toxic drug therapy. Thus, such data that is available today is not actionable in a medically therapeutic relevant way. To make such data actionable, one must have recorded data that allows a specific rhythm diagnosis, and a vague recording hinting that something may be wrong with the heart will not suffice. Further, the recorded data must not only identify the heart-related event of concern, but the signals before and after the event, which provides critical medical information for a physician to diagnose the disorder specifically. Finally, the recorded data must be made certifiable, so that the relationship of the recorded data to the patient that the physician is seeing is clear and appropriately identifiable as an event originating in the patient being examined. Establishing this relationship of data-to-patient has become a legally mandatory step in providing medical care, which heretofore has been impracticable insofar as one cannot merely rely upon a smartphone to provide legally sufficient identification of an abnormality with actionable data such that a patient undergoes a serious medical intervention.
Even once ECG monitoring data of sufficient length and quality to serve as a basis for a diagnosis is obtained, further challenges exist in providing an efficient and actionable interpretation of the data. While a physician may personally perform an over-read of the data over the entire length of the monitoring manually, such an over-read consumes a significant amount of time that will slow down delivering any necessary treatment to the patient. While automated interpretation techniques exist, such techniques still have significant limitations in recognizing certain types of cardiac conditions. For example, such techniques may have trouble recognizing atrial fibrillation (“AF”), a condition characterized by a rapid, irregular, beating of the atrium. AF is associated with an increased risk of stroke and heart failure, and is thus an important condition to timely diagnose. Most automated algorithms trying to diagnose AF focus on individual features of the ECG waves, such as particularly focusing on distances between R-waves and comparing them to predefined thresholds. Such an approach ignores other manifestations of AF and may lead to misdiagnosis AF is initially diagnosed by an absence of organized P-waves 11 and confirmed by erratic ventricular rates that manifest in an ECG R-R interval plot as a cloud-like pattern of irregular R-R intervals due to an abnormal conduction of impulses to the ventricles.
Therefore, a need remains for an extended wear continuously recording ECG monitor practicably capable of being worn for a long period of time in both men and women and capable of recording high quality atrial and ventricular signals reliably.
A further need remains for facilities to integrate wider-ranging physiological and “life tracking”-type data into long-term ECG and physiological data monitoring coupled with an onboard ability to cascade into the medical records and to the medical authorities appropriate medical intervention upon detection of a condition of potential medical concern.
A still further need remains for a flexible way to detect atrial fibrillation based on results of an ECG monitoring results that allows to take into account diverse manifestations of atrial fibrillations on an ECG trace.